First, for quick background: Shopkick works with big retailers including Best Buy, American Eagle, Macy's, Target, and others, offering access to special deals and allowing users to collect points called "Kickbucks," which are redeemable for real-money rewards, like gift cards.

You earn points for walking into participating stores -- verified by a special beacon in each store -- and for scanning barcodes within stores, as instructed by the app. The main idea is to get more people to walk into stores more often, so they'll consider buying something. Shopkick only gets paid when it brings people into the store, and when people buy stuff using a Shopkick deal.

Now, for the stats...

Shopkick, which launched last August, has attracted 750,000 users through January. That's up from 530,000 users at the end of December, and 280,000 at the end of November. That's smaller than Foursquare, Facebook Places, etc. But it's solid.

Some 10% of Shopkick users are active on a daily basis; 20% on a weekly basis, and 40% on a monthly basis. Shopkick also says it retains users 6-7X better than average lifestyle apps.

Business Insider chart

Shopkick is doing 1 million "check-ins" per day. (In much shorter time than it took Foursquare to reach that level of activity.)

But Shopkick isn't really about check-ins -- it's about generating foot traffic to retail stores, so people might consider buying something. ("Check-ins" and "walk-ins" are separate stats; "walk-ins" being worth much more than "check-ins," which are worth very little.)

So how is that working?

Shopkick won't say how many walk-ins it's doing a day for the 1,100 stores and 100 malls in 18 markets that it's installed in.

But 20% of all Shopkick users who live in an area with Shopkick walk-in rewards have already walked into a store with the app on, Shopkick CEO Cyriac Roeding tells us. ("We expected 2%.")

Roeding also says that Shopkick has discovered one way to reliably increase in-store walk-ins -- by boosting the Kickbucks walk-in rewards that Shopkick users would get when they walk into the stores. (We've noticed that these promotions also tend to come with an iPhone push notification, which announces the deal. That may help too.)

One of its retail partners increased Shopkick walk-ins by 68% on Cyber Monday (an online shopping day) over Black Friday (an offline shopping day) by tripling its walk-in Kickbucks reward for the day.

And, on average, these experiments with five different retailers have boosted Shopkick walk-ins by 50% to 100%. Roeding says, "We expected 5%, and retailers would have been happy about that."

This is important because tripling Kickbucks awards only costs the retailer about 50 cents to $1 -- which can very quickly pay for itself as people start shopping. Roeding has told us in the past that a transaction lead in specialty retail is generally worth $10 to $15.

"It definitely drove traffic into the stores," Sports Authority CMO Jeff Schumacher told the WSJ. Sports Authority is extending Shopkick into all of its stores now.

And a Best Buy rep tells the WSJ that "'the return is really positive' given the cost of implementing the system," adding that many Shopkick users seem to be redeeming their Kickbucks for Best Buy gift credits -- a win-win for the chain.

So it looks like Shopkick is actually doing well!

While it doesn't get as much attention as Groupon, Foursquare, and Facebook Places, it seems to be doing good work -- so far, at least -- for its initial retail partners. The actual numbers -- walk-ins, purchases, revenue, etc. -- are still probably small. But retailers are going to be investing heavily in mobile, so Shopkick is in a good position to continue winning deals.

Chains may develop their own apps, too, but will they also build out entire rewards platforms like Shopkick's? They may try, but most will probably do a bad job. So there may be a good reason to work with an aggregator like Shopkick.

Looking ahead, we'll have to see how Shopkick can continue to grow and evolve as Facebook and Foursquare push deeper into the mobile deals and rewards areas. And, further in the future, as mobile payments -- not just deals and rewards -- become part of the equation. Starbucks has taken the lead there, and Google and Apple seem to be preparing their products for launch.